1. Technology Field
The present invention generally relates to x-ray generating devices. In particular, the present invention relates to an integrated fluid pump that simplifies tube design while enhancing replacement options when replacement of pump components is required.
2. The Related Technology
X-ray producing devices, such as x-ray tubes, are extremely valuable tools that are used in a wide variety of applications, both industrial and medical. For example, such equipment is commonly employed in areas such as medical diagnostic examination and therapeutic radiology, semiconductor manufacture and fabrication, and materials analysis.
Regardless of the applications in which they are employed, x-ray tubes operate in similar fashion. In general, x-rays are produced when electrons are emitted, accelerated, and then impinged upon a material of a particular composition. This process typically takes place within an evacuated enclosure of the x-ray tube. Disposed within the evacuated enclosure is a cathode, or electron source, and an anode oriented to receive electrons emitted by the cathode. The anode can be stationary within the tube, or can be in the form of a rotating annular disk that is mounted to a rotor shaft which, in turn, is rotatably supported by a bearing assembly. The evacuated enclosure is typically contained within an outer housing, which also serves as a reservoir for a coolant, such as dielectric oil, that serves both to cool the x-ray tube and to provide electrical isolation between the tube and the outer housing.
In operation, an electric current is supplied to a filament portion of the cathode, which causes a cloud of electrons to be emitted via a process known as thermionic emission. A high voltage potential is placed between the cathode and anode to cause the cloud of electrons to form a stream and accelerate toward a focal spot disposed on a target surface of the anode. Upon striking the target surface, some of the kinetic energy of the electrons is released in the form of electromagnetic radiation of very high frequency, i.e., x-rays. The specific frequency of the x-rays produced depends in large part on the type of material used to form the anode target surface. Target surface materials with high atomic numbers (“Z numbers”) are typically employed. The target surface of the anode is oriented so that the x-rays are emitted as a beam through windows defined in the evacuated enclosure and the outer housing. The emitted x-ray beam is then directed toward an x-ray subject, such as a medical patient, so as to produce an x-ray image.
Generally, only a small portion of the energy carried by the electrons striking the target surface of the anode is converted to x-rays. The majority of the energy is instead released as heat. It is important to remove as much of the excess heat produced during x-ray production so as to prevent heat related failures in the x-ray tube and its components. One common technique for removing heat is to submerge the evacuated enclosure in a coolant contained within the volume defined by the outer housing. The coolant absorbs heat from surfaces of the evacuated enclosure during tube operation.
Under certain circumstances, the ambient placement of a coolant about the evacuated enclosure by itself may not adequately cool the evacuated enclosure. For example, the coolant, such as a dielectric oil or similar medium, may stagnate or thermally pool in certain areas of the outer housing volume, thereby preventing adequate cooling to occur. One area of an x-ray tube that is prone to this phenomenon is located between the adjacent x-ray transmissive windows of the evacuated enclosure and outer housing. Thermal pooling in this region can cause extreme heating of the localized coolant, resulting in intermittent boiling of the coolant. This can result in the creation air bubbles within the coolant and thereby adversely affect the quality of the images produced by the x-ray tube.
To avoid such problems, x-ray tubes often circulate the coolant to prevent thermal pooling and to optimize heat transfer. For example, a fluid pump can be used to circulate the coolant within the outer housing volume. In other implementations the heated fluid can be extracted from the outer housing by the fluid pump and transferred to a heat exchange device, which cools the fluid before it is reintroduced into the outer housing volume. This type of arrangement provides a closed circulation cooling loop useful in removing excess heat from the x-ray tube and preventing problems associated with thermal pooling.
In some x-ray devices, the fluid pump is positioned a distance apart from the outer housing in an unattached configuration. In such a configuration, fluid communication between the outer housing and the fluid pump is achieved via fluid lines. Conversely, in other designs the fluid pump is attached as a complete unit directly to an exterior surface of the outer housing. In either configuration the fluid pump is a self-contained unit and is independently operable with respect to the x-ray tube. As such, should replacement of the fluid pump be necessary, the entire pump is removed, as a unit, from its unattached location or from the outer housing exterior. A new pump is then positioned in place of the previous pump and connected as needed.
X-ray tube cooling systems utilizing pump systems such as these, while functional, can be a relatively expensive option. For example, pump malfunction typically requires replacement or refitting of the entire fluid pump. This wholesale pump replacement occurs despite the fact that many components of the pump may not need to be replaced. Moreover, many such self-contained pumps include welded pump bodies. Should selective replacement of interior components in a welded pump be desired, it is first necessary to grind down or otherwise remove the welds in order access the interior components. After replacement of the components, re-welding must then occur. This process represents a significant expenditure of time and expense.
In light of the above, a need exists in the art wherein a coolant contained within the volume created by a housing of an x-ray tube can be effectively circulated by a fluid pump, so as to effect efficient cooling of x-ray tube components, such as the vacuum enclosure. Such circulation would preferably be accomplished via a fluid pump that has a simplified design and is integrated with the structure of the housing in a manner that reduces the need for complete pump replacement in the event of servicing and repair.